This invention relates to earth boring by the rotary system and more particularly to the securement of a wear sleeve about a length of drill pipe by means of an adhesive plastics material layer molded in situ between the sleeve and drill pipe tube.
Heretofore a variety of means and methods have been employed for the securement of a wear sleeve to a drill pipe tube, as described in some detail in U.S. Pat. Nos. 3,667,817--Kellner; 3,697,141--Garrett; 4,146,060--Garrett; 4,171,560--Garrett; and the references cited therein. One problem that arises in connection with the securement of a wear sleeve to a drill pipe tube by means of adhesive plastics material is the shrinkage of the plastics material as it cures or sets. Such shrinkage tends to leave voids in the plastics material layer between the sleeve and tube. Sometimes the plastics material layer pulls away from the tube or sleeve. This reduces the strength of the connection between the sleeve and tube and may impair the mechanical insulation between sleeve and tube afforded by the plastics material layer which serves to prevent overstressing of the tube.
It has been stated in U.S. Pat. No. 2,180,695--Rembert, that the annulus between a coupling and two adjacent pipe ends can be filled by pouring fluent material into a funnel feeding the annulus at one end and allowing displaced air to exit a funnel at the other end, enough fluent material being poured to rise in both funnels at the end of pouring, whereby on cooling and contracting of the filling material in the annulus additional fluent material may be drawn from the funnels to fill the annulus. This apparatus and procedure is employed however with a filling which is either melted to render it fluent and cooled to harden it, e.g. asphalt, petroleum still residue, high boiling plastic waxes and resins, lead, or sulfur based mixtures, or is initially a fluent mixture of solid particles and water which sets by hydration of the solids, i.e. Portland cement.
Thermoplastic materials that would soften at moderately high temperatures which may be encountered in the heat of the sun or the depths of a well would not be suitable for securing a wear sleeve to a drill pipe tube.
Lead has a melting point of 621 degrees F. For the attachment of wear sleeves to drill pipe tubes it would be of advantage to employ a filling that is fluent at room temperature.
Because of the axial stresses and shock loads imposed on such wear sleeves, Portland cement would not be suitable for securing a wear sleeve to a drill pipe tube.
Regardless of which of the materials proposed by Rembert is selected and despite the provision of inlet and outlet funnels, it will be observed that because all of the filling materials employed by Rembert solidify by cooling or hydration, the material in the funnels may solidify before the larger volume of material in the annulus, thereby preventing the supply of liquid material from the funnels to the annulus when the latter material solidifies and shrinks.